package Date1204;

import java.util.Scanner;

public class Demo3 {//计算圆的面积 结果保留7位小数
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer n = sc.nextInt();
        System.out.println(String.format("%.7f",Math.PI*n*n));
    }
    
}
